The use of disposable diapers has become widespread, and recently leak proof materials such as side gathers, waist gathers, etc., have been provided thereto to prevent sideways leakage to the thighs or leakage to the waist and lower back of urine and soft feces. Sanitary napkins that feature side gathers to prevent sideways leakage of the menstrual flow have also appeared on the market. A high level of water repellency is required of these leak proof materials to prevent the permeation of urine and menstrual flow. Because such materials also come into direct contact with the skin, they must feel soft and have excellent texture.
Conventionally, a nonwoven fabric, etc., obtained by a spunbond process using a thermoplastic resin such as a polyolefin polymer has been used for such members, but there is still considerable room for improvement in terms of softness and texture.
Many proposals have been made to satisfy the above requirements, and there have also been many technical improvements. For example, a fiber or filament comprising polyolefin that is first treated with an alkyl phosphate ester and then with a polysiloxane has been proposed in Patent document 1.
Alternatively, a heat-bondable fiber having deposited thereon a fiber treatment agent comprising a silicone-based component and an ethylene oxide-added alkyl amine component has been proposed in Patent document 2.
Even with the above technical improvements, there is still room for modification and greater practicality from the viewpoint of achieving both antistatic properties and a high level of water repellency. For example, if an alkyl phosphate ester is used as an antistatic agent in Patent document 1, the antistatic properties are insufficient in the step of processing the fiber into a nonwoven fabric, and because a calendar roll process is used to obtain the nonwoven fabric, it is very difficult to obtain a nonwoven fabric with high bulk and good texture with that method. On the other hand, with Patent document 2 the ratio of the silicone-based component in the fiber treatment agent is relatively low, and even though the ethylene oxide-added alkyl amine imparts additional water repellency, a sufficiently high level of water repellency is still difficult to obtain. Generally speaking, when the bulk of a nonwoven fabric becomes high, the density of the constituent fibers tends to decrease, and the water repellency of the nonwoven fabric tends to decrease as well. Therefore, it is difficult to obtain a high bulk, highly water repellent nonwoven fabric using fibers whereon a fiber treatment agent with such a composition has been deposited.
[Patent document 1] Japanese Patent No. 2908841
[Patent document 2] Japanese Patent Application Publication No. H5-321156